1. Field of the Invention
This invention relates to extermination of those species of insects whose life cycle includes a pupation stage.
2. Background of the Invention
Among the more troublesome insects for humans are the fleas (order Siphonaptera of the class Insecta). Humans, particularly in the western United States, suffer from bites of various rodent, rat and squirrel fleas of the genera Xenopsylla, Diamanus and Nosopsyllus, the first of which transmits the bacterium which causes bubonic plague. More commonly, however, humans are susceptible to the irritation caused by the bites of the human fleas (Genus Pulex) and the cat and dog fleas (Ctenocephalides felis and C. canis); Atkins, Insects in Perspective, pp. 481-483 (1978); Johnson et al., Principles of Zoology, pp. 444-445 (1977); Davies, "Insects" in Larousse Encyclopedia of Animal Life, p. 147 (1967);. Flea bites normally provoke an allergic reaction which may include reddish pimples, painful and weeping swellings and intensely itching rashes. Those persons who are particularly sensitive or allergic may suffer extremely severe reactions.
People who have dogs and cats as household pets are only too familiar with the problems that fleas cause. Fleas readily get into the fur of a pet and are carried into the pet owner's residence, shop, store, etc. by the pet. When the pet subsequently lies on a carpet or piece of furniture such as an upholstered chair, bed, sofa or the like, the fleas can move into the fabric of the carpet or furniture. Similarly, if the female flea has laid eggs in the fur of the pet, the eggs and/or hatched larva can be transferred from the pet to the fabric. When the pet's owner thereafter comes in contact with the carpet or furniture, he or she is bitten by the fleas.
Over the years much time and effort has been expended to rid residences and other buildings of flea infestation. Exterminators have used a wide variety of insecticides in water sprays and in powdered form to apply to carpet and furniture; Hamm, The Handbook of Pest Control, Part I (1982); Metcalf, "Insecticides in Pest Management," in Metcalf et al. (eds.), Introduction to Insect Pest Management, Ch. 7 (2nd Edn.: 1982). Of the principal active ingredients of these sprays and powders have been various types of adulticides and larvacides which kill fleas at one or more of the larva, juvenile or adult stages, and insect growth regulators, which when applied to larvae prevent the larvae from pupating and reaching an adult stage, thus halting the reproductive cycle; Cremlyn, Agrochemicals, Chs. 4, 6, and 14 (1991). These efforts have had varying degrees of success, but none has been found to be completely successful in providing universal extermination to a treated population. This lack of overall success has been due to the fact that fleas (and many other similar insects) pupate.
The four-stage life cycle of a flea is schematically illustrated in FIG. 1. During the adult phase the male and female fleas mate and the female lays eggs, which may be laid directly in carpeting, furniture fabrics, the fur of pets or similar locations. The eggs hatch into worm-like larvae. The larvae initially have an insect growth regulating hormone, the amount of which gradually diminishes in a larva over the length of the larval period. This progressive loss of hormone eventually triggers the beginning of pupation, in which the larva forms a cocoon or cuticle around itself, and within the cocoon becomes a pupa. Over a course of the pupation period thereafter the pupa is metamorphosed inside the cocoon into a juvenile flea, which essentially has the adult morphology but is immature. Within a short period of time, the juvenile matures into an adult flea. Both juveniles and adults can bite. (For brevity herein, the term "adult" will often be used to include both adults and juveniles, since for the purposes of this invention both are susceptible to adulticides.) Four-stage life cycles such as those of fleas are well known and have been widely described in the literature; Atkins, supra, Ch. 9; Evans, Insect Biology: A Textbook of Entomology, Ch. 4 (1984); Friedlander, The Biology of Insects, Ch. 3 (1976); Arms et al., Biology, pp. 501-502 (1979); Villee, Biology, pp. 205-208 (3rd Edn.: 1957); and Farb, The Insects, Ch. 3, (1962). For the purposes of this inveniton, oherein, the life cycle of the flea (and similar insects) is significant because during the pupation stage the fleas are substantially unaffected by any of the prior art methods used for flea extermination and control of flea infestations.
Therefore, when the adult fleas, eggs and larvae infest carpeting or furniture fabrics, the resulting pupa become lodged in those materials and locations. Application of water-based insecticidal sprays or insecticidal powders are normally sufficient to kill adult fleas, larvae and flea eggs, to the extent that the insecticides contact the targets, either directly during application or subsequently as residues. Many sprays and powders cannot, however, penetrate deeply into the weave of fabrics or the depth of carpet pile and therefore frequently do not contact eggs, fleas or larvae. Even those that do penetrate, however, will kill only eggs, fleas or larvae there, but will not affect the pupae in their cocoons, even by direct contact. Consequently, one normally finds that while a flea infestation appears to have been dealt with adequately immediately after an application of the spray or powder insecticides, within a short time thereafter the pupation phase of the unaffected pupa is completed and the location is again infested by newly hatched juvenile fleas and subsequently by adult fleas, follow which the entire cycle repeats.
It is known that pupa can remain dormant for extended periods of time, and that the end of pupation and opening of the cocoon is triggered by elevated levels of ambient humidity, temperature and pressure; Silverman et al., Ann. Entomol. Soc. Am., 78:763-768 (1985); Rust et al., J. Mod. Entomol., 26:301-305 (1989); Dryden, "Biology of Fleas on Dogs and Cats", 3rd UCR Urban Pest Mgmt. Conf. (Riverside, Calif.: Mar. 29, 1994). Applications of water-based insecticides and powdered insecticides do not markedly affect the humidity, temperature and pressure of the pupal cocoon environment, and therefore have no effect on causing the cocoons to open. Common events that might provide increases in humidity, temperature or pressure, such as steam cleaning of carpets or upholstery, often serve to increase flea infestation rather than decrease it, since steam cleaning causes many of the pupal cocoons to open, thus adding to the overall flea population. While there has been one prior art method incorporating a borate into steam, that has also been ineffective in eradicating juvenile and adult fleas. Borates are solely larvacides, so that when the steam/borate is applied, the larvae are killed, but the pupal cocoons are simultaneously stimulated to open, thus producing a new population of adult fleas which are unaffected by the borate. The new population of adult fleas seek an animal or human host and once again begin the life cycle.
Consequently, prior art methods for "exterminating" fleas and similar insects have been ineffective for long term pupa elimination, providing not complete extermination but at best merely periodic diminishing of flea populations. The populations, however, return as the flea life cycle continues and the resident pupae hatch to new fleas.